The disclosure relates to a method for operating a hydraulic vehicle brake system which has a master brake cylinder with a controllable brake booster.
Laid-open patent application DE 103 27 553 A1 discloses such a hydraulic vehicle brake system which, with the exception of the brake booster, is of conventional design. The vehicle brake system has a dual-circuit master brake cylinder to which four wheel brakes are connected divided into two brake circuits. A dual-circuit vehicle brake system is not compulsory for the disclosure, just as a plurality of wheel brakes is not compulsory. In addition, the known vehicle brake system has a wheel slip control device for which terms such as (brake) anti-lock control device, traction control device, vehicle movement dynamics control device and/or stability control device as well as the abbreviations such as ABS, TCD, VMDC, ESP are customary. The hydraulic part of the wheel slip control device comprises a brake pressure-increasing valve and a brake pressure-decreasing valve for each wheel brake, as well as, for each brake circuit, a hydraulic pump, a separating valve with which the master brake cylinder can be disconnected hydraulically from the brake circuit, and an intake valve by means of which the master brake cylinder can be connected to a suction side of the hydraulic pump for the purpose of quickly increasing the brake pressure. Such wheel slip control devices and their method of functioning are known per se and will not be explained in more detail at this point.
Instead of a partial-vacuum brake booster, the known vehicle brake system has an electro-mechanical brake booster with a hollow-shaft electric motor whose rotor has a nut of a spindle drive, which nut converts the rotational driving movement of the electric motor into a translatory movement for activating the master brake cylinder. Other designs of an electro-mechanical brake booster are possible for the disclosure, for example the brake booster can have a toothed rack gearing system, preferably with a worm for driving the toothed rack, for converting the rotational driving movement of an electric motor into a translatory movement for activating the master brake cylinder. An electro-mechanical brake booster with a linear motor, an electromagnet or a piezo-element can also be used for the method according to the disclosure. The enumeration is not exhaustive.
The vehicle brake system is an auxiliary force brake system, i.e. an activation force for activating the master brake cylinder is applied partially as a muscle force by a vehicle driver and also as an extraneous force by the electro-mechanical brake booster. Operation as an extraneous force brake system is also conceivable, in which extraneous force brake system the activation force is generated exclusively as an extraneous force by the brake booster and a muscle force which is applied by a vehicle driver activating the brake, or else an activation travel which is carried out by the vehicle driver, serves as a setpoint variable for performing open-loop or closed-loop control of the force of the brake booster which is referred to as an extraneous force.